EP2801467A1 - Calibration device for calibrating an extruded tubular film - Google Patents

Abstract

Calibration device (15) for calibrating an extruded film tube (8) above the freezing limit, wherein an annular gap is formed between the calibration device (15) and the film tube (8) a plurality of calibration segments (16) distributed around a longitudinal axis (L) and forming a central through-hole (26) for passing the film tube (8) along the longitudinal axis (L), the calibration segments (16) for adjusting the diameter of the passage opening (26) are adjustable, and at least one outlet nozzle per calibration segment (16), through which a calibration gas is supplied to the passage opening, wherein the discharge nozzles are designed such that the calibration gas is at least approximately parallel to a surface of the film tube supplied to the annular gap and the annular gap in a single flow direction of the gaseous medium is flowed through.

Description

The invention relates to a calibration device for calibrating an extruded film tube above the frost boundary, wherein an annular gap is formed between the calibration device and the film tube, comprising a plurality of Kalibriersegmente which are arranged distributed about a longitudinal axis and form a central passage opening for passing a film tube along the longitudinal axis, wherein the Calibration segments for adjusting the diameter of the passage opening are adjustable, and at least one outlet nozzle per calibration segment, through which a gaseous medium is fed to the passage opening.

Contacting calibration devices with roller arms are known as calibration means, which are adapted to the diameter of the film bubble via various adjustment devices. For older types, such as in the DE 26 38 744 A1 described, consist of the foil contacting calibration means of bent rods on which a plurality of small rings is arranged, which are set by the film contact in rotation. This design is extremely susceptible to contamination and leaves depending on the degree of contamination at the separation points of the Teflon rings markings and even surface damage to the film.

In newer improved designs, the aforementioned design of the calibration is replaced by straight, ball-bearing rollers. For example, is from the DE 20 2005 006 532 U1 known to provide a plurality of rollers with approximately horizontal axis and substantially to the round film tube tangential arrangement, wherein the rollers are circumferentially distributed in a plurality of superimposed planes. The rollers form a polygon cross section in plan view, which forms a passage opening for the film tube. The rollers are radially adjustable, so that the diameter of the passage opening can be adapted to the diameter of the film tube. The rollers are rotatably disposed in contact with the film tube and around the horizontal axes to avoid marks on the film tube. For the roll surfaces, materials are used which prevent adhesion of the film tube to the rolls, such as Teflon, nylon, silicone or the like. If a structured roll surface is desired, also foam, felt or the like are used.

The film tube is extruded from a thermoplastic and vaporizes waxy components (monomers) that can settle on the rollers of the calibration. Thus, there may be increased resistance to rotation of the rollers. Furthermore, the sheathing contaminate after some time and leave markings, provided that no regular cleaning or replacement of the roll shells takes place.

Furthermore, there are non-contact calibration devices in which solid, non-rotatable guide body are provided as calibration instead of the rollers from which an air curtain is blown from a microporous surface in the direction of the film bubble to prevent film contact. Such embodiments are eg in EP 1 488 910 B1 and WO 2005/084919 A1 described in detail.

These constructions are extremely susceptible to contamination because the porous surface is easily clogged by oily monomers outgassing from the melt film in the extrusion process in combination with dust from the ambient air. Also, the absolute freedom from contact is not always guaranteed, since the directed at right angles to the film tube speed vector of the diffusing air curtain is small and is not always sufficient as a counterforce when the film tube in systems with high performance by the speed of the blown in the hose forming zone cooling air in high-frequency movements is offset.

To avoid these disadvantages suggests EP 0 143 154 A1 a calibration device having an annular support member which the film tube from the outside encloses. The support member is provided with inwardly open annular channels having terminals for supplying cooling air. The annular channels are bounded by flanks, wherein in the annular channels such an amount of air is blown that the air flowing over the side flanks forms a the air-cushion removed from the withdrawn film tube. This ensures that the film tube does not come into contact with the support element.

DE 36 37 941 A1 shows a device for aftercooling and calibrating guiding a film tube above the frost limit of the film tube. This comprises a surrounding the film tube and not touching the tube ring, which has on its directed against the film tube inside bladder holes, which are directed to the film tube. The hose ring may in this case consist in the circumferential direction of individual sheet sections and be made of a material that allows deformation and thus adapting the hose ring to different diameters of the film tube.

A calibration device of the type mentioned above disclosed EP 0 273 739 A1 , The calibration device comprises a calibration ring which completely surrounds the film tube, or a plurality of calibration segments which run over part of the circumference of the film tube. These each have two inwardly directed slot-shaped openings, wherein one of the slot-shaped openings in the withdrawal direction of the film tube and one of the slot-shaped openings is aligned opposite to the withdrawal direction of the film tube. The two slot-shaped openings are also directed away from each other, so that between the two openings a zone of low pressure or a zone of partial vacuum is formed. This zone of low pressure serves to attract the film tube to the Kalibriersegment, wherein the exiting through the slit-shaped openings air streams each form an air cushion, which is prevented by the film tube touches the Kalibriersegment. In addition, the surface of the Kalibriersegments is set back in the region of the zone of low pressure compared to the other the film tube facing surfaces of the Kalibriersegments, so that this also ensures that the film tube does not touch the Kalibriersegment.

A disadvantage of the known embodiments is that the air is introduced either in a direction transverse to the surface of the film tube to this, whereby an immediate force is exerted on the film tube, which can lead to a deformation or to instability of the film tube. Or it is as according to EP 0 273 739 A1 , Zones of low pressure present, which can lead experience according to a pulsating movement of the film tube, which in turn affects the stability of the leadership of the film tube.

The object of the present invention is to propose a calibration device which ensures stable guidance of the extruded film tube.

The object is achieved by a calibration device according to claim 1. Preferred embodiments will be apparent from the dependent claims.

In this case, it is particularly advantageous that the discharge nozzles are designed such that the calibration gas is supplied to the annular gap at least approximately parallel to a surface of the film tube. Thus, there is no direct force component of the Kalibriergasstroms on the film tube. In the non-contact calibration device according to the present invention, the Venturi or Bernoulli effect is used, through which a calibrating gas flow guided at a sufficient speed tangentially along a surface of the calibration segment facing the film tube supplies a sucking and fixing force to a sufficiently close moving element Case of the film tube exerts, without there being a touching contact between the film tube and one of the Kalibriersegmente. By virtue of this force in conjunction with the calibration gas cushion, the film tube assumes a stable distance position from the calibration segment as a counter force.

Furthermore, the design of the exhaust nozzles prevents such that the annular gap is traversed by the calibration in a single flow direction, that forms a central zone of low pressure or a partial vacuum, the pressure of which deviates from the pressure within the flow of the calibration, so that an instability of the Foil tube or a pulsating movement of the film tube is avoided.

The flow through the annular gap in exactly one flow direction also has the advantage that a plurality of superposed calibration segments do not influence each other, since the entire flow direction of all calibration segments and thus the entire calibration device is identical.

The calibration segments are arranged distributed in a plan view in the direction of the longitudinal axis. They may well be spaced apart along the longitudinal axis. Viewed from above, the passage opening through which the film tube passes through the calibration device results.

The calibration gas is preferably air. In principle, however, other gases or gas compositions can be used.

Preferably, the calibration segments are designed such that ambient air is sucked into the annular gap on an inflow side of the calibration device. As a result, an amplification of the air flow takes place, i. A larger amount of calibration gas or air is passed through the annular gap, as calibration gas is supplied to the annular gap. Thus, energy can be saved, since a smaller amount of calibration gas must be provided.

To achieve this, a certain flow rate of the calibration gas is required. The flow velocity can be increased by designing at least one blow-off nozzle for each calibration segment to be slit-shaped in the form of a blow-out gap. In this case, the blow-out gap preferably has a gap width of less than one millimeter. It has turned out to be particularly advantageous if the blow-out gap has a gap width of less than 0.5 mm.

In order to ensure that the calibration gas does not have to be made available to a high pressure, which would also reduce the energy efficiency, it is preferable to provide that the blow-out gap has a gap width of more than 0.2 mm.

To ensure the intake of ambient air as efficiently as possible, can be provided that the exhaust nozzles are arranged outside the passage opening. This means that the calibration gas flows at least partially outside the passage opening and thus can entrain ambient air.

For this purpose, it can be provided that the at least one discharge nozzle for each calibration segment blows out the calibration gas along a contour surface which merges into a guide surface within the passage opening. Ambient air can thus be entrained in the area of the contour surface.

In this case, the calibration segments can be designed such that the calibration gas blown out of the blow-off openings follows the course of the contour surface. The contour surface may in this case be part of an outer surface of the respective Kalibriersegments. The contour surface is preferably bent, preferably convex, at least partially for deflecting the flow of the gaseous medium. The curved part of the contour surface preferably has a radius of at least 4 mm, preferably from 4 mm to 10 mm.

Here, the so-called Coander effect is used, after which a fluid has the tendency to run along a convex surface without detaching from the surface and moving in the original flow direction. What is important here is that a jet follows and flows along the convex surface, so that the jet of the fluid flows within e.g. the ambient air, which is at rest, moves. As a result, the jet of fluid does not detach from the convex surface, as would happen with a normal flow where all ambient air flows along the convex surface.

In the case of the calibration device according to the invention, it may be advantageous for the outlet nozzles to blow out the calibration gas transversely to the longitudinal axis, preferably at right angles to the longitudinal axis.

In order to ensure a sufficient speed of the calibration gas after exiting the exhaust nozzles, they are connected to at least one pressure source. Basically, this can be a compressed air source. However To be able to use an inexpensive source of pressure, such as a fan, and thus to avoid a costly provision of compressed air, it can be provided that the pressure source, the gaseous medium with a pressure of less than 0.5 bar, preferably below 0.2 bar Provides.

The calibration segments are preferably designed arcuate about the longitudinal axis. In principle, however, the calibration segments can also be straight.

Furthermore, it may be provided that adjusting means are provided, by means of which the volume flows and / or the temperature of the calibration gas streams emerging from the calibration segments per calibration segment can be controlled or regulated separately.

It is also possible to arrange a plurality of calibration segments one above the other, wherein the superimposed calibration segments are adjustable to different diameters of the passage opening, so that the passage opening along the longitudinal axis and along the film tube, e.g. tapered in the withdrawal direction of the film tube in order to take into account shrinkage effects of the film tube during solidification can.

Figur 1

eine Seitenansicht einer Folienblasanlage;

Figur 2

eine Aufsicht auf eine erfindungsgemäße Kalibriervorrichtung in zwei unterschiedlichen Stellungen der Kalibriersegmente, und

Figur 3

einen Querschnitt durch eines der Kalibriersegmente der Kalibriervorrichtung gemäß Figur 2.

A preferred embodiment is explained below with reference to the figures. Hereby shows:

FIG. 1

a side view of a Folienblasanlage;

FIG. 2

a plan view of a calibration device according to the invention in two different positions of the Kalibriersegmente, and

FIG. 3

a cross section through one of the calibration segments of the calibration according to FIG. 2 ,

FIG. 1 shows a side view of a blown film 1. On a bottom 2 is an extruder 3, to which two feed hoppers 4, 5 for thermoplastic material recognize. In granular form via the feed hoppers 4, 5 abandoned thermoplastic material is plasticized and homogenized by pressure and additional heating means in a screw of the extruder 3 and pressed into a subsequent to the extruder 3 Blaskopf 6 with a vertical axis. The blowing head 6 has on its upper side 7 a ring nozzle, not recognizable here, from which an expanding longitudinal axis L axisymmetric film tube 8 emerges from initially still plasticized thermoplastic material. The film tube 8 is inflated after exiting the annular nozzle with air, to which an air inlet 9 is used, which is disposed within the annular nozzle and is located within the film tube 8. Thus, the still plastifiable film tube is widened. After solidification of the plastic material of the film tube 8 of this substantially maintains its diameter. The film tube 8 is pulled along the longitudinal axis L further up in the withdrawal direction A and flattened in a Flachlegevorrichtung 10 and led away via a stripping 11 upwards. The flattened film tube 8 is then wound up on coils.

Immediately above the blowing head 6, a cooling ring 12 is provided with internal outlet nozzles 13, from which cooling gas flows out and the film tube 8, which is under increased internal pressure, flows annularly substantially band-parallel. The plasticized in this area film tube 8 expands initially in diameter under said pressure in the interior until it solidifies under the action of the cooling gas and assumes a constant diameter. The location of the transition from the plasticized plastic material to the solidified plastic material is called the freezing limit and is indicated by the reference numeral 14. Above, ie in the withdrawal direction A downstream of the freezing boundary 14, there is a calibration device 15, which comprises a plurality of calibration segments 16, which are arranged in a ring around the longitudinal axis L and around the circumference of the film tube 8. In order to allow adaptation to film tubes 8 of different diameters, the calibration segments 16 are fastened to a support frame 17 so as to be adjustable approximately radially relative to the longitudinal axis L. The calibration device 15 is a contactless calibration device 15 whose components do not come into contact with the film tube 8. For this purpose, each calibration segment 16 is connected via calibration gas lines 18 with a fan 19. The fan 19 blows air into the Kalibriergasleitungen 18 to the individual Kalibriersegmenten 16, wherein have the Kalibriersegmente 16 in later explained in more detail exhaust nozzles that blow out the air or other gaseous medium in the direction of the film tube 8. The calibration gas lines 18, which lead to the individual calibration segments 16, are fed by a common main line 20. Flow flaps 21 are respectively arranged in the calibration gas lines 18 in order to be able to control the calibration gas flow within the individual calibration gas lines 18. Thus, the volume of Kalibriergasströme and possibly also, not shown here heating elements, the temperature of the Kalibriergasströme to the individual Kalibriersegmenten 16 segmentally controlled by a controller 22, so that the volume flow and / or the temperature of the calibration gas segment per segment over the circumference can be set variably.

FIG. 2 shows the calibration device 15 in a plan view perpendicular to the longitudinal axis L. Overall, eight calibration segments 16 are provided, which are shown in two different positions. As already explained above, the calibration segments 16 are adjustable approximately radially relative to the longitudinal axis L. In FIG. 2 the Kalibriersegmente 16 are shown in a radially outer position and in a radially inner position.

The support frame 17 is viewed in alignment annular and arranged around the film tube 8. On the support frame 17, the Kalibriersegmente 16 are pivotally mounted, wherein in the following one of the Kalibriersegmente 16 is described by way of example for all other Kalibriersegmente.

The Kalibriersegment 16 is fixedly connected at one end thereof to one end of an arm 23, wherein the remote from the Kalibriersegment 16 end of the arm 23 is pivotally mounted about a pivot axis S on the support frame 17. The pivot axis S runs parallel to the longitudinal axis L. The arm 23 is tubular in shape to be able to carry calibration gas. At the end facing the pivot axis S, the arm 23 is conductively connected to a calibration gas line 18 so that calibration air from the calibration gas line 18 can flow into the arm 23. At the side remote from the pivot axis S, the arm 23 is connected to the calibration segment 16 such that calibration air can be introduced from the arm 23 into the calibration segment 16. The calibration segment 16 is also tubular. By doing Calibration segment 16 bores 25 are provided, through which the calibration air is supplied to a not shown here and later explained in more detail exhaust nozzle, which is used for a contactless guiding and calibrating the film tube 8.

The calibration segment 16 is in plan according to FIG. 2 designed arcuate and has an inwardly facing guide surface 24, which is adapted to the largest possible diameter of the film tube 8. All Kalibriersegmente 16 are arranged distributed around the longitudinal axis L and include the film tube 8 between them. Together, the individual ring segments 16 form a ring with a central through-opening 26 for passing the film tube 8.

The Kalibriersegmente 16 can each be pivoted about the pivot axis S inwardly, so that the passage opening 26 in diameter decreases iris-shaped, as shown in the second position inside. In the inner pivot position, the arms 23 together with Kalibriersegmenten 16 are pivoted in the direction of arrow P inward, so that a film tube 8 can be calibrated with a smaller diameter.

In principle, other adjustment possibilities for the calibration segments 16 are conceivable, such as scissor mechanisms or radially extending linear drives. It is also possible in principle that the Kalibriersegmente16 are not arcuate but rectilinear.

FIG. 3 shows a cross section through one of the Kalibriersegmente 16, wherein the cutting plane is aligned parallel to the longitudinal axis L. The Kalibriersegment 16 is designed in the form of a hollow profile and forms a Kalibriergaskanal 27, which is fed by the Kalibriergasleitung 18 with calibration gas, wherein the flow directions of the calibration gas are indicated by the arrows shown in the calibration gas 27. The calibration gas is supplied from the calibration gas channel 27 through the bores 25 in a first side wall 30 of the calibration segment 16 to a slot-shaped outlet nozzle 28 in the form of a blow-off gap, the calibration gas subsequently emerging from an outlet opening 29. The exhaust nozzle 28 extends approximately the entire length of the Kalibriersegments 16 over part of the circumference of the Foil tube 8, wherein the exhaust nozzle 28 is fed by the plurality of holes 25 with calibration gas. The exhaust nozzle 28 is formed by the first side wall 30 and a nozzle plate 31 which is externally attached to the first side wall 30. The first side wall 30 has an outer surface 33 to which the nozzle plate 31 is fixed, the nozzle plate 31 having an inner surface 32 which faces the outer surface 33 and which is spaced therefrom so that the exhaust nozzle 28 is in shape forms a blowout gap. The outlet opening 29 faces the film tube 8, wherein the outer surface 33 of the first side wall 30 is arranged perpendicular to the longitudinal axis L and thus transversely to the film tube 8.

The outer surface 33 has a flat course within the outlet nozzle 28 and, starting from the outlet opening 29, transitions in the direction of the film tube 8 into a contour surface 34, which partly has a curved course. The curved course of the contour surface 34 merges with the guide surface 24 of a second side wall 35 pointing inwards. The guide surface 24 is in the in FIG. 3 aligned cross-section parallel to a surface 37 of the film tube 8, so that forms a gap between the guide surface 24 and the film tube 8, which is based on all ring segments 16 over the entire circumference an annular gap 36.

The calibration gas is thus deflected through the bore 25 and the exhaust nozzle 28 and flows within the exhaust nozzle 28 and also shortly after emerging from the outlet opening 29 transverse to the film tube 8 and parallel to the contour surface 34 of the first side wall 30. It forms a curtain-shaped Kalibriergasstrahl very limited thickness, which flows parallel to the outer surface 33. Due to the Coander effect, this calibration gas stream does not tear off the outer surface 33, but follows the contour surface 34 and is thus deflected in a direction parallel to the film tube 8 into the annular gap 36. Here, ambient air is entrained on an inflow side of the calibration device 15 from below the Kalibriersegmente 16, so that there is an air reinforcement. The gas volume ultimately flowing through the annular gap 36 is a multiple of the volume of calibration gas leaving the outlet opening 29.

Due to the high flow velocity of the gas within the annular gap 36, a Venturi effect results, which attracts the film tube 8 to the guide surface 24, the film tube 8 does not touch the guide surface 24, since the gas flowing through forms an air cushion. Thus, the film tube 8 can be kept at a constant distance from the guide surface 24 and be guided and calibrated in total.

Among other things, the Coander effect depends on the flow velocity and the thickness of the flow jet or flow curtain on calibration gas. It has been shown that good effects can be achieved if a pressure of less than 0.5 bar, preferably of less than 0.2 bar, is set within the calibration gas channel 27. Particularly advantageous is then a gap width of the exhaust nozzle 28 of less than 1 mm, preferably less than 0.5 mm and preferably of more than 0.2 mm. The radius of the bent part of the contour surface 34 is at least 4 mm in cross-section, preferably 4 mm to 10 mm. LIST OF REFERENCE NUMBERS 1 Blown Film 2 ground 3 extruder 4 hopper 5 hopper 6 blow head 7 top 8th film tube 9 air intake 10 Flattening device 11 off unit 12 cooling ring 13 exhaust nozzle 14 Frost limit 15 calibration 16 Kalibriersegment 17 supporting frame 18 calibration gas 19 fan 20 main 21 flow flap 22 control 23 poor 24 guide surface 25 drilling 26 Through opening 27 Kalibriergaskanal 28 Ausblasdüse 29 outlet opening 30 first sidewall 31 nozzle plate 32 palm 33 outer surface 34 contoured surface 35 second side wall 36 annular gap 37 surface L longitudinal axis A withdrawal direction S swivel axis P arrow

Claims (16)

Calibration device (15) for calibrating an extruded film tube (8) above the freezing limit (14), wherein an annular gap (36) is formed between the calibrating device (15) and the film tube (8), comprising a plurality of calibrating segments (16) arranged around a longitudinal axis (16). L) are distributed and form a central passage opening (26) for passing the film tube (8) along the longitudinal axis (L), wherein the Kalibriersegmente (16) for adjusting the diameter of the passage opening (26) are adjustable, and
at least one exhaust nozzle (28) per calibration segment (16) through which a calibration gas is supplied to the lead-through opening,
characterized,
in that the discharge nozzles (28) are designed such that the calibration gas is supplied to the annular gap (36) at least approximately parallel to a surface of the film tube and the gaseous medium flows through the annular gap (36) in a single flow direction. Calibration device according to claim 1,
characterized,
that the Kalibriersegmente (16) are designed such that ambient air is drawn on an inflow side of the calibrating device (15) into the annular gap. Calibration device according to one of the preceding claims,
characterized,
that the at least one outlet nozzle (28) is designed according Kalibriersegment (16) slot-shaped in the form of a Ausblasspalts. Calibration device according to claim 3,
characterized,
that the Ausblasspalt has a gap width of less than 1 mm, preferably less than 0.5 mm. Calibration device according to one of claims 3 or 4,
characterized,
that the blow-out gap has a gap width of greater than 0.2 mm. Calibration device according to one of the preceding claims,
characterized,
that the blow-out nozzles (28) are arranged outside the through-opening (26). Calibration device according to one of the preceding claims,
characterized,
in that the at least one discharge nozzle (28) per calibration segment (16) carries the calibration gas along a contour surface (34) which is in a guide surface (24) within the passage opening (26) passes, blows out. Calibration device according to claim 7,
characterized,
that the Kalibriersegmente (16) are designed such that the out of the blow-out nozzles (28) follows blown span the course of the contour surfaces (34). Calibration device according to one of claims 7 or 8,
characterized,
in that the contour surface (34) is an outer surface (33) of the respective calibration segment (16). Calibration device according to one of claims 7 to 9,
characterized,
that the contour surface (34) is bent at least in part for deflecting the flow of the calibration gas. Calibration device according to claim 10,
characterized,
that the bent part of the contour surface (34) has a radius of at least 4 mm. Calibration device according to one of claims 7 to 11,
characterized,
that the blow-out nozzles (28) the span transverse to the longitudinal axis (L), preferably at right angles to the longitudinal axis (L), blow out. Calibration device according to one of the preceding claims,
characterized,
that the blow-out nozzles (28) are connected to at least a pressure source (19), said pressure source (19) provides the calibration gas at a pressure of below 0.5 bar, preferably below 0.2 bar, is available. Calibration device according to one of the preceding claims,
characterized,
that the Kalibriersegmente (16) about the longitudinal axis (L) are arc-shaped. Calibration device according to one of the preceding claims,
characterized,
in that setting means (21) are provided by means of which the volume flows and / or the temperature of the calibration gas emerging from the calibration segments (16) per calibration segment (16) can be controlled or regulated separately. Calibration device according to one of the preceding claims,
characterized,
that a plurality of calibration segments (16) are arranged one above the other and
in that the superimposed calibration segments (16) are adjustable to different diameters of the passage opening (26).

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